Anatomy of the January 5 Thames Storm Surge

The Waikato Regional Council have produced draft report on the Jan 5 Storm surge

In summary the storm surge :–

was the highest recorded at Thames (Tararu ) since 1990
was a one-in-200 year event at Tararu
compared to previous events between 1999 and 2014 was 0.43m higher than the next highest event at Thames
was 0.8 m above the predicted king tide

of that 0.8 m – 0.5 m was due to wind setup and wave generation and 0.3 m was due to the “inverse barometer effect” of the low-pressure system
Multiple properties were damaged including one uninhabitable home and 9 with moderate damage on the western coast (Thames Coast) of the Coromandel Peninsula, and there was 13 uninhabitable and 72 moderately damaged houses along the Kaiaua/Miranda coast
Barometric pressure dropped to 987.2 hPa at Tararu, 990.1 hPa at Whitianga,
“demonstrated the high degree of vulnerability of a number of coastal settlements to northerly wind events that are common at this time of year.”

Regional Council Conclusion –

“It is also important to better understand the likely frequency of such events in view of climate change and resulting sea level rise. Although based on current analyses the event was a <0.5% AEP (>200 year return period) at Tararu, 5-2% AEP at Whitianga (20-50 year) it is likely that these events will become more common in the future and alter these frequency relationships.”

The latest MfE Guidance to the Regional Council and other councils spells this out much more clearly than these bland conclusions –
Extreme storm surge events like January 5 will become much more frequent as sea levels rise. Even a rise of 10 cm could turn an extreme storm surge event from every 100 years to every 30 years. Add another 10cm and it could happen every 10 years. Another 10cm on top of that and it is every 3 years.

Inundation (flooding) maps of the event are being produced but were not yet available. If they become available I’ll post them here.

map